The roughly 8 meters of intestine in the adult human plays numerous roles in physiologic homeostasis including absorptive, secretory and immune functions. Commensurate with these essential roles, diseases of the intestine are a considerable source of human morbidity and mortality. Indeed, numerous pathologic conditions including inflammatory bowel diseases, mesenteric ischemia, congenital syndromes and trauma, with or without concomitant intestinal resection, result in “short-gut” syndromes resulting in severe deficiencies of physiologic intestinal function and effective intestinal failure. While enhanced regeneration and/or frank tissue engineering of the intestine is highly desirable in these conditions, no established procedures currently allow robust ex vivo expansion of intestinal epithelium or stem/progenitor cells thereof. Consequently, therapies have currently relied on supportive measures such as total parenteral nutrition, in which all nutrition is provided intravenously, or intestinal transplantation.
The intestine is an organ with tremendous regenerative potential, whereby stem cells resident in proliferative crypt regions give rise to progenitors capable of multilineage differentiation. The intestinal stem cells (ISCs) are able to repopulate epithelium of the entire 8-meter length of the adult human intestine every 5-7 days, helping to maintain the integrity of the mucosal barrier and effecting tissue repair upon injury. It has been postulated that the ISC niche has complex architectural requirements whereby myofibroblasts enveloping the proliferative crypt provide essential signals to crypt stem and/or progenitor cells.
A significant impediment to restorative intestinal regeneration for therapeutic purposes has been a lack of clear understanding of the signals regulating self-renewal and proliferation of intestinal stem and progenitor cells, although progress has been made with the identification of the role of Wnt signaling; and the ability of R-spondin1 (RSpo1) to strongly induce intestinal proliferation in vivo.
A second and perhaps more significant impediment to intestinal tissue engineering has been a notable lack of in vitro culture systems allowing the growth of intestinal epithelial cells for more than about 10 days.